A typical method for producing an alkaline battery includes the steps of:
(A) inserting at least one positive electrode pellet into a cylindrical battery case with a bottom and pressing the positive electrode pellet to form a cylindrical positive electrode having a hollow and adhering closely to an inner face of the battery case;
(B) inserting a cylindrical separator with a bottom into the hollow of the positive electrode inside the battery case;
(C) injecting an electrolyte into the separator to impregnate the positive electrode and the separator with the electrolyte;
(D) filling a gelled negative electrode into the separator;
(E) inserting a negative electrode current collector into the negative electrode; and
(F) sealing an opening of the battery case.
In Patent Document 1, in the step (B), a cylindrical separator with a bottom is inserted into the hollow of the positive electrode inside the battery case. This separator includes: a wound cylindrical portion; and a bottom portion that is substantially U-shaped in cross-section, the bottom portion covering an opening of the cylindrical portion at a lower end of the cylindrical portion and having an upstanding portion that extends along a lower inner face of the cylindrical portion.
However, when the battery is dropped or subjected to a large impact or vibrations during transportation or the like, the gelled negative electrode flows, thereby displacing the bottom portion of the separator. As a result, the negative electrode may leak from between the cylindrical portion of the separator and the upstanding portion of the bottom portion of the separator, thereby causing an internal short circuit.
To prevent such leakage of the negative electrode, in Patent Document 2, a cylindrical separator with a bottom is inserted into the hollow of the positive electrode inside the battery case in the step (B). This separator includes: a wound cylindrical portion; and a bottom portion that is substantially U-shaped in cross-section, the bottom portion covering an opening of the cylindrical portion at a lower end of the cylindrical portion and having an upstanding portion that extends along a lower outer face of the cylindrical portion.
In Patent Document 3, the bottom portion of the separator of Patent Document 1 and the bottom portion of the separator of Patent Document 2 are combined to form a separator having two bottom portions, and the lower end of the cylindrical portion of the separator is sandwiched between two upstanding portions of the bottom portions of the separator.    Patent Document 1: Japanese Laid-Open Patent Publication No. 2009-163982    Patent Document 2: Japanese Laid-Open Patent Publication No. Hei 11-329396    Patent Document 3: Japanese Laid-Open Patent Publication No. 2005-071908